Comparative tree height measurement using different instrument
Sara Pariyar, Ram Asheshwar Mandal
The height measurement is very complicated and time consuming job in forestry. The measurement value may differ with use of different instruments but research related to this using different instrument wasn’t conducted so far in Nepal. Thus, this research was objectively carried out to assess the variation in height measurement using Clinometer, Rangefinder and Abney level and error caused by the use of instruments, their precision level in height measurement to find the most efficient instrument for measurement. Satyadevi community forests in Chitwan district was selected as the study site. Total 110 healthy plants were measured, representing different diameter class 5 cm and above 55 cm with interval of 5. Each class consist 10 plants whose heights were measured. The bamboo pole was used to find the actual height of the plant for diameter class 5-30 cm. The measurement of big diameter class was measured applying destructive techniques. The time was recorded for each measurement according to instrument used. Data were analyzed using statistically to compare the height using different instruments with actual measurement. Error was estimated using the differences between the values and precision was also calculated. The time efficiency was calculated using mean time and estimator (E%)²×T. Furthermore, the regression analysis was done to show the correlation between actual height and estimated height measured by instruments. The result showed that, the average value of height of plants were 5.42 ± 1.77, 5.57 ± 1.47 and 5.17 ± 1.7 m using Clinometer, Rangefinder and Abney level respectively in 5-10cm diameter class which values were 23.81 ± 1.77, 21.79 ± 1.47 and 22.98 ± 1.7m measured by Clinometer, Rangefinder and Abney level respectively in diameter >55 cm. The differences in mean value between diameter class 5 to >55 cm with comparison to true height measured with Clinometer ranges from 0.16 to 2.74 m whereas measurement with Rangefinder ranges from 0.12 to 1.22 m and 0.10 to 1.88 m for Abney level. The average error percentage is lower with the measurement taken by Rangefinder with the value 2.95% and higher with the measurement taken by Clinometer with the value 8.27%. The average error percentage of measurement taken with Abney level is 4.31%. The average precision of height measurement with instruments shows that Rangefinder is higher than Abney level and Clinometer with very small difference of 0.01 and 0.005 simultaneously. The Rangefinder is the most efficient height measuring instrument since the efficiency value was found to be lowest 842.08 in comparison to estimated value of it using Clinometer and Abney level with 8029.30 and 2378.42 respectively. Since, R² value of true height and measured height using Rangefinder was 0.70 whereas Clinometer was 0.66 and of Abney level was 0.61. It was found that, measured height using Rangefinder performed the most correlated with true height of the plant. This research will be useful for choosing the instrument according to precision and time efficiency required.